the 204 has the same turn time as a 757the 204s pax capacity is slightly smaller than the 757the speed is within .01 mach

The only major difference is the really weak range of the 204...

the 204 uses a ton more fuel than the 737

That "only difference" is a mighty big one, since range is ultimately the defining characteristic between most aircraft. Compared to the TU-204...

A 752 seats about 10% more passengers.A 752 consumes about 20% less fuelA 752 can carry those passengers almost twice as far.

A 10% increase in revenue with a 20% decrease in fuel costs is HUGE. That's north of a 20% per-seat pricing advantage over the competition -- i.e. where a 757-200 could turn a profit at $100/seat, a TU-204 would need to charge $120.

Now compare the TU-204 with a 737-400:

A 734 seats about 10% fewer pax, so you lose revenue, BUTA 734 uses a full 35% less fuelA 734 still manages to have significantly more range than the Tu204, in the range of 200-1000NM moreA 734 takes only HALF the turnaround time (which can easily make up for the 10% fewer pax in many cases)A 734 requires 1200ft less runway to land, the Tu204 runway req limits its capacity at many locations, reducing its pax advantage greatlyA 734 requires 20% less flight attendant staffA 734 is much closer in upfront costs and, after consider major maintenances, will likely cost less in fixed costs than a TU204 and save many tens of millions more in variable costs

In the end, a TU-204 is FAR more closer to the 737 than a 757. It's a a 734 that seats 18 more people, sucks about 35% more fuel, doesn't fly as far, and needs more runway and staff to operate.